test: consolidate suites and remove redundant cases (#1459)

Regression tests were scattered across feature- and bug-specific files, and some suites repeated the same checks. Group tests by responsibility, isolate feature fixtures in test classes, and remove duplicate or obsolete cases.

The review covered all 127 collected test modules on main. This reduces them and removes or combines definitions:.

 No application code changes.

CONTRIBUTING.md

@@ -112,6 +112,18 @@ Use `pytest` to run tests locally:
 uv run python -m pytest -vs --cov src --cov-report term-missing tests/
 ```
 
+Group tests by the module or cohesive subsystem they exercise. Add regression tests to the
+existing suite and use descriptive test classes to separate features, edge cases, and integration
+scenarios. Scope feature-specific fixtures to their test class, especially autouse fixtures that
+could change unrelated tests. Create another test file only for a distinct responsibility or
+when the existing suite would become unwieldy; avoid one file per bug or pull request.
+
+For example, keep time-window model tests in `tests/test_configabc.py`, measurement channels
+and persistence in `tests/test_measurement.py`, and GENETIC0 parameter preparation in
+`tests/test_genetic0params.py`. Keep provider-specific suites and unit/system tests separate.
+When moving tests, verify that parametrized cases and fixture behavior are preserved with
+`pytest --collect-only` and an execution of the affected suites.
+
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